Unravelling genomic diversity of Zygosaccharomyces rouxii complex with a link to its life cycle.

Zygosaccharomyces rouxii and the related species Zygosaccharomyces sapae (hereafter referred to as Z. rouxii complex) are protoploid hemiascomycete yeasts relevant in the elaboration and spoilage of foodstuff. Divergence of Z. rouxii complex before whole genome duplication, leading to the genus Saccharomyces, makes these yeasts very attractive for genome evolution study. Relatively little is known, however, about the diversity in this branch at the genetic and physiological levels. In this work, we investigated Z. rouxii complex, encompassing strains that in other works have been studied separately and comparing them in a comprehensive way. We showed that the majority of strains are unusually heterogeneous in their ribosomal DNA, a signal of relaxation of concerted evolution. Further analysis showed that they have hypervariable karyotypes, different levels of ploidy, and that housekeeping markers vary both in copy number and sequence. Overall, the results provide compelling evidence that the strains considered in this study are a complex of haploid, aneuploid and diploid mosaic lineages. The reproductive mode and life cycle of Zygosaccharomyces could lead to this unsuspected diversity.